A REVIEW OF NITROGEN INFLATION....
OF PNEUMATIC TIRES
By: Harold J Herzlich
This REVIEW will focus in on accepted scientific principles and peer
reviewed scientific papers that form the basis for an expected nitrogen
tire inflation customary and usual practices paradigm shift.
In a recently published article in Tire Business, Herzlich stated the
following: "Nitrogen’s slower permeability
characteristics coupled with its bone-dry nature may partially ameliorate
some field abuse conditions, including long term inflation maintenance
neglect, improper repairs and certain types of tire pressure monitor
malfunctions. Even though high purity nitrogen is no guarantee of
performance and will not undo the many forms of damage or abuse that can
lead to tire failure, it offers a low cost, risk free and positive service
opportunity that has finally become commercially and technically
practical". Based upon published long term
oxidation tire weakening theories accepted by the scientific community,
the required 95%+ level of nitrogen purity in the tire
should be a primary consideration if the long term benefit of this
technology is to be fully realized.
A 1970 paper by L Sperberg, "Tire Durability With Nitrogen
Inflation" documented various durability and service advantages for
this method. The subject with regard to the general motoring public
remained dormant since a reliable, cost effective and safe nitrogen source
was not available.
In 1998 Bridgestone, Firestone took a positive nitrogen inflation
position: (Technical Bulletin P-047-X). stating that "nitrogen is
acceptable as an inflation gas for use in Bridgestone and Firestone
passenger, light truck and truck tires."
In 2000, a well known independent consultant to truck fleets, Peggy
Fisher issued the statement that "Air May Be Out For Tire Inflation" and
reinforced all opinions regarding the benefits of nitrogen tire inflation
In 2003 Bridgestone took a stronger proactive position advocating dry,
high purity nitrogen inflation (Should You Stop Putting Air In Your
Tires, Vol 8, Issue 3, www.trucktires.com).
Cited advantages were:
1. Less inflation Loss ("six months to lose 2 psi with nitrogen compared
to just a month with air")
2. Less Inflation Pressure Fluctuation ("tires inflated with wet air tend
to run hotter and fluctuate in pressure more")
3. Reduced Wheel Corrosion ("oxygen corrodes aluminum and steel wheels...
.rust can clog valve stems, causing them to leak")
4. Safety ("nitrogen is used in off-highway and aircraft tires ...which
can run so hot they can actually catch on fire").
Michelin, BF Goodrich, Uniroyal, Riken, Cavalier issued a joint Technical
Bulletin in November, 2003 which stated that, "Michelin supports the
use of nitrogen on its ability to better retain air over a period of
Goodyear, in a June 14, 2004 Product Service Bulletin #2004-09 stated,
"Goodyear supports the use of nitrogen, as an inflation gas, in all
Goodyear, Dunlop, Kelly, and Associate Brand and Private Brand products,
based on the ability for the tire to retain pressure for a longer period
of time. The use of nitrogen will not affect the tire warranty".
In 2005, The Retread Information Bureau issued a news release, "Why
Inflating Tires With Nitrogen Makes Sense" and included the statement, "By
extending the useful life of a tire, retreading offers additional
In Europe, there have been additional activities supporting the nitrogen
inflation concept. Air Liquide in France claimed
a... "25% improvement in tire life since tires stay inflated longer
because nitrogen migrates 3 times slower than air and nitrogen eliminates
internal oxidation of the tire so more retreads can be achieved."
Liquide claimed... 30% savings on tires
While aircraft tires have a unique set of needs that include pressure
retention, non-explosive inflation gas, no moisture and excellent
recappability, their required use of the inert high purity nitrogen
validates its’ desirability in all pneumatic tires.
Numerous articles since the 70's have shown advantages for nitrogen
inflation and its’ beneficial effect on the retention of the tire
components’ original properties.
In a September 20, 2004 technical article in the largest international
rubber industry trade paper, Rubber and Plastics News, Dr. J Baldwin of
Ford presented his peer reviewed findings "Passenger Tires Inflated
With Nitrogen Age Slower". Some of his conclusions included, "lower
permeability than oxygen (better gas mileage), more controlled inflation
pressure due to the absence of moisture, expected improvement in
structural durability due to significant reduction in rubber oxidation
(oxidation caused by air from the cavity being forced into the tire
Herzlich, a tire industry consulting Chemical Engineer with 50 years
industry experience stated in a Tire Business Article October 24, 2005
that "Nitrogen’s slower permeability characteristics coupled with its
bone-dry nature may partially ameliorate some field abuse conditions,
including long term inflation maintenance neglect, improper repairs and
certain types of tire pressure monitor malfunctions. Even though high
purity nitrogen is no guarantee of performance and will not undo the many
forms of damage or abuse that can lead to tire failure, it offers a low
cost, risk free and positive service opportunity that has finally become
commercially and technically practical".
As already noted, nitrogen inflation of tires is not new. For many years
very high pressure bottled high purity nitrogen was the only source used
to inflate tires having critical service requirements (i.e.: aircraft,
giant earthmover and race cars).
The real world of tire durability and fuel economy performance is complex
and includes a large population of tires that have been exposed to a wide
range of damaging service conditions that cause excessive deflection
(distortion and heat generation) which accelerates oxidative and thermal
degradation. Nitrogen inflation will not undo many forms of tire damage
that lead to failure.
Both oxidation and thermal weakening (not aging) of the tire structure are
scientifically accepted mechanisms that can contribute to some common
types of tire failures. Under inflation, which is a major contributor to
the oxidation/thermal degradation process, also results in reduced tread
life and increased fuel consumption. Under inflation results in the higher
rolling resistance that pollutes the air as it unnecessarily burns
hundreds of millions of gallons of fuel each year. Under inflation creates
other safety issues such a marginal and unpredictable vehicle
High purity nitrogen inflation, by partially
addressing some of these issues and concerns, may bring about an important
paradigm shift in tire maintenance practices. As its’ value is
communicated and accepted by the public and regulatory officials, high
purity nitrogen inflation can become the state of the art practice for
tire service operations.
ECONOMIC ADVANTAGES FOR HIGH PURITY NITROGEN INFLATION
Air is composed of about 78.1% nitrogen and about 20.9% oxygen. Air
also can contain significant and variable levels of water vapor and
contaminants from the compressor system. Since oxygen diffuses through
rubber at about 3 times the rate of nitrogen, a tire will retain its
pressure longer when inflated with high purity nitrogen. Herzlich showed
that 96% nitrogen tires stored for 30 days at a range of elevated
temperatures lost 2.2% less pressure than similar tires inflated with air.
While this appears to be a small difference, one must consider this effect
over a much longer period of time and with different tire sizing
configurations and with tens of millions of tires.
The effect of tire inflation pressure on fuel economy is apparent to any
person riding a bicycle with under inflated tires. A range of peer
reviewed tire industry papers confirm that under inflation is a serious
and common reality that diminishes auto safety for a variety of reasons. T
Laclair, Michelin, Tire Science and Technology, "Truck Tire Operating
Temperatures on Flat and Curved Test Surfaces" Vol 33, No. 3. Laclair
states that "operating temperature is critical to the endurance life of a
tire". Under inflation is a critical heat contributing tire
Oxidation of rubber follows the basic laws of
chemistry. The rate of chemical oxidation is highly dependent upon
temperature and roughly doubles for every 18 degrees increase in the tires
operating temperature. Under inflation raises the operating temperature of
the tire; thereby increasing the rate of its oxidative weakening. Higher
ambient temperatures (ie: Southwest) add significantly to the thermal
stress created by under inflation.
BF Goodrich scientists documented additional inflation information in a
paper by Beatty and Miksch,"Some Effects of Tire Inflation On Radial
Tire Performance", Rubber Division, ACS, Las Vegas, NV, Paper 45, May
Weeks and Sheets, Effects of Tire Pressure and
Performance Upon Oil Use and Energy Policy Options", Proceedings of the
Intersociety Energy Conservation Engineering Conference, 1991,
estimated that a tire with 28% under inflation (25 psi instead of 35 psi)
would consume about 3.8% more fuel over a 100,000 mile service life span
of the vehicle. They based this upon data that showed a force
resisting the rolling of the tire to be about 18 pounds for a 35 psi tire
vs. 26 pounds rolling resistance for the same tire at 25 psi inflation.
This would calculate out to about $70 per year per
vehicle of increased fuel cost. When one adds the shorter tread
life for the over deflected tire, one can easily estimate a significant
added cost coupled with reduced reliability when running moderately under
Tracey and Waddell of Exxon in their published 2004
International Tire Exhibition and Conference paper, "Halobutyl
Innerliners Offer Best Tire Durability", reported that a 20%
deficiency in tire inflation pressure reduced durability by 20%.
Coddington of Exxon in his paper, Tire Inflation
Pressure Loss, Its Causes and Effects, 5th Australasian Rubber Technology
Conference, quantified under inflation deficiency stages. He also
demonstrated the temperature variability of pressure loss and the greater
tendency for small tires to be more severely affected. The mini-spare
high pressure tire is very vulnerable to this high surface to low volume
Volvo Cars Nederland RV in a press release "Nitrogen in Auto Tires
Helps the Environment and Safety. Volvo Prefers Nitrogen in Auto Tires
(Volvo Prefereert Stiksof in Autobanden)" Volvo stated that
"scientific research has proven that the use of nitrogen as inflation gas
for auto tires gives many advantages compared to normal compressed air. A
tire with 20% under inflation uses 2 to 3% more fuel than a tire with the
proper pressure. Volvo Cars Netherlands expects that the Volvo dealers
will follow and implement this environmentally beneficial initiative ...
every tire is eligible to be filled with nitrogen." Volvo is a
division of Ford Motor Company.
Based roughly upon about 206 million passenger cars and light trucks in
operation (and estimating 25 gallons saved annually by each vehicle)
proper inflation would reduce annual gasoline
consumption by about 5 billion gallons and eliminate the air pollution
created by 15 million tons of unnecessary gasoline combustion.
The increased muscle energy required to move the bicycle with soft tires
is an example of the increased fuel needed to move a vehicle with "soft"
tires. While the power of the engine masks the negative effect on rolling
resistance, the simple observation of the vehicles increased pep after an
oil change is usually mistakenly attributed to the "clean oil" that was
just put into the engine. Actually it is more likely due to the tires
being aired up during the express oil change service.
The presence of moisture in the inflation air of tires causes deviations
in the way the inflation pressure changes as the tire operates. Dry high
purity nitrogen eliminates moisture caused deviations in tire pressure.
Moisture and oil in the compressed air system makes the valve core and/or
the pressure monitoring device less reliable. Allegations of expensive
damage or critical malfunction to the pressure monitoring device will be a
matter of increasing responsibility to people servicing tires. Dry
nitrogen will reduce the validity of certain claims.
CHEMICAL FACTORS JUSTIFYING HIGH PURITY NITROGEN INFLATION
Oxygen, while necessary for life, is in reality an aggressively
corrosive gas that attacks the rubber molecule and other critical
chemicals in the tire as it dissolves and diffuses through the structure.
Depending upon the nature of the rubber molecule, the oxidative process
irreversibly weakens the tire Hunter, Datta and Noordermeer from the
Netherlands in their Rubber Chemistry and Technology Literature Review
Article of 2004, Vol 77, No. 3, Pg 476 " Addressing Durability of Rubber
Compounds" identified the accepted oxidation chain reaction responsible
for weakening process. The literature also describes the diminishing
effects of antioxidant additives over longer periods.
The detrimental effect of oxygen on the fatigue and fracture properties of
rubber has been demonstrated by studies that show faster rates of crack
growth, shorter fatigue life and greater susceptibility to severe strains.
While tire "aging" has become a topic of interest with regard to long term
tire reliability and durability, the chronological age of a tire by itself
has little bearing on the tires weakening process that is associated with
actual failures. The weakening of general purpose rubber such as used in
tires is an oxidation/service condition process. Abusive service
conditions such as under inflation or overloading accelerate the
Uniroyal paper 18D17 "Long Term Durability of Tires by N Tokita"
established that "one reason for loss of long term durability is
oxidative reactions in the breaker stock during service ... the tear
strength of the breaker stock excised from the oxygen aged tires for
unaged, accelerated aged and accelerated aged showed rubber deterioration,
whereas the tire filled with pure nitrogen showed little.. ....From these
laboratory tests, we conclude that the oxidative changes of the breaker
stock is a inevitable cause of the limited service life." This paper
finds that the decrease in the relative rubber strength relates to an
increase in oxygen absorbed.
A Goodyear Tire and Rubber Company paper presented at the International
Tire Exhibition and Conference (2004) by Dr. M Cohen, "How Tires Age
and How To Characterize Aging In Tires" demonstrated a steady increase
in oxygen content at the belt-edge from sets of consumer tires that were
in service for longer service periods. The effect of oxygen content on the
reduction of laboratory fatigue life was significant as the oxygen content
increased. Laboratory studies showed "faster crack
growth in air (100 kilocycles) than in a nitrogen atmosphere (450
kilocycles). Data also demonstrated that higher inflation pressure
accelerated the rate of oxygen take-up. This will become more important as
tire pressure specifications will increase for improved fuel economy (now
as high as 51 psi (350 kPa) in some passenger tires.)
Baldwin, J M, (Baldwin, JM, Bauer, DR, Ellwood, KE, Passenger Tires
Inflated With Nitrogen Age Slower, Rubber and Plastics News, September
20, 2004) clearly established that passenger tires inflated with nitrogen
age slower. In his work, "tires inflated with 96 percent and 99.9
percent nitrogen were oven aged at 60C (140F) for three to twelve weeks.
For comparison, tires inflated with either air (80%/20% or 50%/50%)
nitrogen/oxygen were oven aged alongside the nitrogen inflated tires".
"The tires inflated with more than 95 percent
nitrogen do not appear to change very much from the new tires even after
12 weeks in the oven, whereas the tires inflated with the oxygenated media
change dramatically, even after three weeks in the oven." Further
analysis validated Baldwin’s conclusions that, "...tires inflated with
more than 95 percent nitrogen do not appear to change very much from new
tires." After twelve weeks of this very aggressive laboratory aging
condition, Baldwin concluded that, at 12 weeks tires inflated with 96
percent nitrogen......the beginning of oxidative degradation can be seen.
Nitrogen inflated tires, however degrade far slower than tires inflated
with the oxygenated media.
It is based upon this 96 percent nitrogen
finding that it is not recommended to exceed 4 or 5 percent oxygen in the
Other Baldwin conclusions were "the oxidation of the steel belt
rubber is truly driven from the contained air pressure .... the skim may
be oxidized slightly from the outside when nitrogen filled, but the rate
of degradation is significantly lower than when the tire is filled with
air" Baldwin demonstrated that the peel strength
changes in the 95 percent nitrogen exposed samples progressed at a much
slower rate than the samples exposed to air. The fact that he was still
able to see very slow oxidation in the 95 percent nitrogen exposed samples
amplifies the expectation of a loss of the nitrogen durability benefits as
one goes to lower levels of purity.
Baldwin states: "The overall conclusion of the study is:
When nitrogen is used as the inflation media, the
change in rubber properties is significantly slowed down or even halted."
Based upon the above findings
gas purity level monitoring of the nitrogen
generation process is an important part of the nitrogen inflation process.
TIRE TEST RESULTS NHTSA
The Department of Transportation DOT has under review tire
manufacturers recommendations of an endurance wheel test using 50% oxygen
enriched inflation gas to accelerate the long term oxidation weakening of
tires. This in itself adds weight to the potential value of inert pure
nitrogen gas inflation.
Coddington showed a significant improvement in oxidation resistance and
tire durability when a nitrogen gas was used in place of air. In his
"Factors in Tubeless Radial Tire Durability" June 1993, he described work
by N Tokita which found that "oxygen aged tires showed a major reduction
of strength while those inflated with nitrogen showed slight loss.
Test data that was reported under varied aging conditions showed:
Relative Strength, %
34 - 38
N2 20 cycles
84 - 90
N2 aged 110hrs/115C
Coddington also reported tire data:
Wheel Test Hours To Failure
215 hours, 240 hours
no failure, 600 hours
Listed below are probable real world advantages for high purity nitrogen
Innerliner violations such as improper repairs, punctures, impact
damage and bead mounting damage take place in tires and the resulting
intra carcass oxidative pressurization is an accepted causation of tire
tread detachments. Regardless of how effective the inner liner is, it
cannot perform when it is violated by service misuse.
Nitrogen, which is bone dry, will also eliminate moisture moving into the
casing and attacking the fabric/ steel reinforcement/ adhesion systems as
well as attacking the wheel/valve/pressure monitoring system.
Run flat tire configurations, which generate higher temperatures while
running disabled, will benefit from a less combustible mix in the violated
air chamber. Medium over the road truck tires with duals are sometimes
subject to very high temperature overload/under inflation running
conditions that can initiate internal combustion within the air chamber.
Pure nitrogen inflation will reduce this combustion possibility.
Truck casings will be in a more recappable, higher value condition because
of their reduced oxidation and under inflation history.
Nitrogen inflation will contribute to the long term storage and durability
of an inflated spare tire which requires optimum pressure retention and
static inflated aging/high temperature storage oxidation resistance.
High purity nitrogen inflation concept will encourage the motorist to be
more aware of specialized high quality tire maintenance. This can be
raised to the same attention level as an oil change schedule. This will
also encourage return visits the dealer (non generic, high quality
nitrogen source) giving opportunity for inspection and ROTATION.
HAROLD J HERZLICH, BChE
HERZLICH CONSULTING, INC.
TIRE ENGINEERING AND CHEMISTRY
New York University, University Heights, Pre-Medical, College of
Engineering, Chemical Engineering - ’56
Southern Connecticut College - Graduate Chemistry Program, Polymer
Chemistry, ASM - Corrosion
University of Wisconsin - Instructions and Warnings
Nevada Community College - Philosophy of Critical Thinking
Quinnipiac College - Graduate Business Program, Marketing Economics,
Export Marketing, Statistical Decision Making, Private Investigator Skills
and Techniques, Private Security Rules & Regulations, Private Security
Alexander Hamilton Business
Miscellaneous - Tire Engineering, Rubber Chemistry, Management,
Quality College, Tire Mechanics and Vehicle Handling, Vehicle Rollover
Mechanics, Aerospace Landing Gear Systems, Sudden Air out , Wet Skid ,
Ice/Snow Traction, Tread Detachment , Mismounting Bead Rupture, Over
Deflection Hysteresis, SEMA 93-04
American Chemical Society, Rubber Division Chairman (‘82), Society of
Automotive Engineers (‘87), American Chemical Society, Rubber Division
Chairman-elect (‘81), Yale Medical School - Medical Ethics Committee,
American Chemical Society, Rubber Division, Treasurer (‘78 - ‘81),
American Chemical Society (‘66), Tire Society (‘83), Rubber Chemistry and
Technology, Business Manager American Academy of Forensic Sciences (‘88),
Rubber Division, Chairman, Membership Committee, Education Committee,
American Assoc for the Advancement of Science (‘94), Rubber Division,
Chairman, Budget and Finance Committee Calif Highway Patrol - Tire Failure
Expert/Lecturer, Charles Goodyear Award Committee, ASM (‘99), Technical
Editor - Tire Industry ITEC Select Founder/Chairman, Elastomed (‘83),
Reviewer - J Wiley, Chemical Technology-Tire Cords Connecticut Rubber
Group, Chair (‘66), Treasurer, Director, Education Invited Reviewer -
Anderson Publishing, Tire Tech Akron Rubber Group, Charter Member Ohio RP
Group Tire Industry Association (‘05), Licensed Private Investigator,
Texas (‘02), A10230, Charter Member of State of Connecticut Highway
Transport Institute, Technical Advisor - Rubber Manufacturers Association,
Reviewer - Polyisoprene in Soviet Union, Chair, Belt Tear Pattern Expert
Peer Review (‘04), Delivered papers and talks to Federal officials and
industry including Rubber Division, AIChE, RMA, AAFS, Akron RG, Boston RG,
Connecticut RG, Southern RG, Washington RG, Chicago RG, Philadelphia RG,
NHTSA, Clemson University, University of Nevada. Yale University,
Chemistry career talks/ local schools, International Tire Exhibition and
Conference, American Chemical Society Law Division Rubber Division,
American Chemical Society, Tire Topical Steering Committee, Patent on
cartable tires. Patent application: Awling. Invented, developed and
manufactured elastic asphalt composition for road repair. Peer reviews
about 250 rubber related technical papers a year. Selects and edits about
50 tire related technical papers a year for presentation to the industry.
Selects and edits rubber related technical papers for global publication,
Pro Bono rubber related technical advice to RPN generated rubber industry
individual, state, federal, military, foreign inquiries. Symposia:
Rubberized Asphalt for Roads, Medical Applications of Rubber,
Creativity/Innovation/Excellence in Mngt, Rolling Resistance of Tires,
Mixing/Calendering Technology, Tire Safety, Rubber Industry Product
Liability , Conference Chairman ITEC1994, 96, 98, 00, 02, 04, 06, Lecturer
Tire Industry Association (‘05) Customary and Usual Industry Practices,
Liability Risk Reduction, Lecturer: Community College of Southern Nevada,
(Management) Practices), Lecturer:, Southwestern Association of Technical
Accident Investigators, 2001 (Tire Technology and Failure Analysis
Protocols), Lecturer TIA, 2001 (tire forensics), Technical responder for
RMA, Technical tire commentator for Public Radio Broadcasting, Petitioner
to NHTSA, Quoted in the FEDERAL REGISTER, Department of Transportation,
Tire Safety 49CFR
Who’s Who in America
Honorary Life Member, American Chemical Society, Rubber Division
American Men and Women of Science
Honorary Life Member, Connecticut Rubber Group
Trilogy Award Committee
G S Whitby Award Nomination
Goodyear Tire and Rubber Company Production Squadron, 7/56
Goodyear Tire and Rubber Company Process Development, 1/57
Armstrong Rubber Company Junior Product Compounder, 2/58
Armstrong Rubber Company Sr. Compounder, 6/61, Division Compounder, 3/62
Armstrong Rubber Company Manager, Passenger Car Compound Development, 5/65
Armstrong Rubber Company Senior Research Chemist, 5/70
Armstrong Rubber Company Manager, Compound Research, 1/73
Armstrong Rubber Company Manager, Compound Development, 7/75
Armstrong Rubber Company Director, Tire Engineering, Legal Matters and
Product Reliability, 1/85
Pirelli- Armstrong Tire Company Director, Tire Engineering, Legal Matters
and Product Reliability, 6/88
Elasphalt Corporation President Herzlich Consulting, Inc. CEO, 1/90
Rubber and Plastics News Technical Editor ITEC (International Tire
Exhibition and Conference) Chairman and Conference Organizer
New York University, United States Army Reserve Officer Training Corp
United States Coast Guard, Critical Tire Engineering Skills Enlistment
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